Leak-proof centerboard construction for sail boats



Dec. 13, 1966 KOENIG 3,291,091

LEAK-PROOF CENTERBOARD CONSTRUCTION FOR SAIL BOATS Filed Dec. 22, 1,9642 Sheets-Sheet 1 [/4 T0 Bow .2 /2- mm x J f 4 Dec. 13, 1966 F. L. KOENIG3,291,091

LEAK-PROOF CENTERBOARD CONSTRUCTION FOR SAIL BOATS Filed Dec. 22, 1964 2Sheets-Sheet 2 United States Patent 3,291,091 LEAK-PROOF CENTERBOARDCONSTRUCTION FOR SAIL BOATS Francis L. Koenig, 5295 Old Dominion Drive,Arlington, Va. Filed Dec. 22, 1964, Ser. No. 420,277 3 Claims. (Cl.114-132) This invention pertains to sail boat construction, andespecially to an improved centerboard mounting system for small sailboats, which will overcome various problems heretofore encountered inthe use of centerboards, lee boards and the like.

The use of retractable centerboards to improve the stability andmaneuverability of boats, which centerboards can be raised to allownavigation in shallow water, is almost as old as the art of boatconstruction itself. In all cases, the board, which is parallel to thevertical plane of the keel or longitudinal center-line of the hull,moves up and down within and beneath a narrow open-bottom enclosurecalled the trunk, and when a single centerboard is employed, itsvertical plane is actually on the centerline of the hull. When two suchboards are employed on either side of the hull centerline, each moves inits own trunk, and the boards are usually referred to as lee boards. Twoboards may also be used on the centerline, in which case one is forwardof the center of hull resistance set up by the sails and the other isaft of this center. Both such boards can be in one long trunk or eachmay have its own trunk. The trunk may be closed at the top, or it may beopen (and above the water line), and some form of pivot for the board isusually provided, allowing the board to be raised and lowered by anattached cable, called the pennant, by manual effort or by a Windlass orwinch.

Smaller boats are usually equipped with a dagger type of centerboard,which as the name implies is thrust up and down through the centerboardtrunk which is open at the top. Other small boats have pivoting orrolling action centerboards, again operated through an open top trunkwith pivoting points or rolling mechanism on the top of theopencenterboard trunk. These devices are either operated by had or through asystem of blocks to provide additional operating power. An open topcenterboard. trunk has many disadvantages; first, it is crude inappearance since the open top trunk and the operating portions of thecenterboard cannot be neatly concealed. Second, the open top trunk withthe centerboard protruding through is a dangerous trap for unwaryfingers. Third, under certain conditions water is-splashed up throughthis open centerboard to the discomfort of passengers and crew. Fourth,in the event of a capsize it is almost impossible to bail out therighted hull without first closing the open-top centerboard trunk, whichwould otherwise allow water to enter the hull as fast as it is bailedout. Fifth, this open topped construction is structurally weak; whenlateral pressure is transferred to the centerboard by the sails, onlyone side of the centerboard trunk reacts, necessitating cumbersomereinforcing members near the open top.

Larger and/or more finished boats have closed top centerboard trunks;this alone answers all of the objections raised above but it requiresthat the centerboard be pivoted on a bolt or other member referred to asa pivotpin, which is usually located near the forward end of thecenterboard trunk, approximately midway between the bottom of the trunkand the top of the trunk cap. The board itself is raised and lowered bya cable attached somewhere aft of the pivot-point, operating upwardthrough a hole in the centerboard cap and connected to a block or Winch.This operating cable is referred to as a pennant. In smaller boats, thepivoting member is somedifilfi l Patented Dec. 13, 1966 times a squareshaft which allows the board to be raised or lowered by lever action,with the lever attached to the end or ends of the square pivoting pinthat protrudes through the centerboard trunk sides, and having suitablebearing bushings therein.

The centerboard pivot-pin is the basic and uncorrectable weakness ofthis type of boat. There is no known method of permanently waterproofingthe area where the pins project through the sides of the centerboardtrunk. The centerboard trunk is narrow, ranging in internal width fromA1 of an inch up. Since the pinhole is above the bottom of the boat byone-half of the breadth of the centerboard, it is almost impossible ofaccess. Since the board must fit snug so as to react properly to thethrust of the sails, there is no room on the interior faces of the trunkfor gaskets, washers, stuifing boxes or similar devices used on otheropenings below the water-line. Normal sailboat maintenance requires thatcenterboards be removed periodically for cleaning, re-painting and forremoving growths and debris from the interior surfaces of thecenterboard trunk. The pin must be removed from the centerboard trunk toallow the removal of the centerboard. Therefore, even if, through theuse of exotic sealants, a boat manages to leave the factory in a fairlywatertight condition, this seal is broken the first time the board isremoved; and since a thorough technical knowledge of epoxy or othersealans is usually beyond the ken of the average boat owner or servicingmechanic, it is usually returned to the water in a leaking condition.This is because the water-proofing can only be applied to the inboardfaces of the trunk, which can be compared to painting the inside of abasement wall to prevent leaks. Water creeps in between the pin andtrunk walls, saturating the trunk material and finding'its way throughdefects in wood or natural openings in fiberglass layers to areas remotefrom the pin.

When under way and under sail, a strain is applied to the trunk walls bythe lever action of the centerboard reacting against the water due tothe sail-pressure, which in turn induces movement or flexing of thetrunk walls in the area of the pin, further aggravating the tendency toleak.

This invention overcomes all of the disadvantages mentioned above, bythe simple procedure of providing for'a fixed sealed pin in the originalconstruction which can be made permanently waterproof because it isnever removed. This invention shows two methods of attachingcenterboards to fixed pins, one with a pin in the upper half of thetrunk and the other with a pin through the trunk just above the innerhull surface. In the case of fiberglass boats, this permanent pin can becast into the hull construction itself; or, an appropriately locatedhole can be drilled through the construction after removal from theconstruction forms, and after insertion of a proper pin, the entire areacan be made water-proof through the use of epoxy sealants and additionallayers of fiberglass over the protruding ends of the fixed pin. Similarprocedures can be used in the case of wood or metal construction. Sincethe pin never has to be removed, it can be welded into place in the caseof metal boats, or, in the case of wooden boats, epoxy or polysulphidesealants can be used at the factory to insure a permanent water-tightinstallation.

It is accordingly a principal object of the present invention to providea centerboard (or lee board) construction which overcomes all of theknown disadvantages of previous arrangements of this type. Specifically,the invention provides a centerboard system which is adaptable either toopen-top trunks or to closed trunks (which often form part of a seat,table or bunk support) and which allows the board to be removed veryeasily from below,

without any risk of leakage through the pivot pin region, and withoutany danger of losing the board accidentally as can happen with variousprior constructions when the boat is moved backwards while the board isstuck in mud or the like. Even when my new centerboard is in the upposition, it cannot be removed unless the pennant is slack, as willappear below, so that its loss by accident is entirely prevented.

Briefly, the above and other objects and advantages of the newconstruction are attained by an arrangement in which the pivot pin ispermanently fixed in the hull of the boat, specifically in the sidewalls of the trunk, so that removal of the board from the pivot does notentail removal of the pin, and it can be permanently sealed in place inwater-tight fashion as an incident of the construction of the hull. Theportion of the centerboard which pivotally coacts with the pin is soconstructed that the desired pivoting motion is obtained without dangerof loss of the board by accident in any conditions of operation, yetwithout interfering with its ready removal, from below, when this isnecessary. Also, the construction ensures that when the board is in itsupper or raised position, there are no projections from the underside ofthe hull, to be broken when the boat is on a marine railway or trailer,or when careened on a beach.

The characteristic features of the invention, and certain preferred waysof practicing it, are described in more detail below, in connection withthe specific embodiments illustrated in the accompanying drawings, inwhich:

FIG. 1 is a vertical section view taken through the centerboard trunk ofa typical boat hull, the centerboard being shown in solid lines and inside elevation.

FIG. 2 is a vertical sectional view taken along line 22 of FIG. 1.

FIG. 3 is an enlarged detail side view of the pivot region of FIG. 1,with the pivot pin itself shown in section.

FIG. 4 is a view looking toward the bottom of the pivot pin block ofFIG. 4.

FIG. 5 is a view similar to FIG. 1 of a modified construction of theparts.

FIG. 6 is a vertical sectional view taken along line 6-6 of FIG. 5.

FIG. 7 is an enlarged section, looking in the same direction as FIG. 5,of a modification thereof.

For purposes of illustration, I have chosen to show the invention asapplied to a hull of glass fiber construction, but it will be understoodthat it is equally applicable to other materials as well. Thecenterboard itself, in the case of a glass fiber hull, would normally beof such material, but this is not an essential requirement. Dependingupon the size of the vessel and other factors, the centerboard may be ofsolid construction (wood, or plate or cast metal), or it may be largelyhollow, and in that case loaded with metal shot, lead or the like as isfamiliar to those skilled in boat construction.

In FIG. 1, a portion of the bottom of the hull is indicated by numeral10, and upstanding therefrom, in the interior of the hull, is the usualcenterboard trunk 12, here shown as having a closed top except for anopening at 14 to allow passage of the centerboard pennant 16 as from awinch 18 to the upper edge of the centenboard 20. At the bottoms of theside walls 22 and 24 of the trunk 12, a fixed pivot pin 26 is provided,the same being integrally cast in place, preferably during theconstruction of the hull, as by being embedded in the glass fiber andresin material of the trunk walls, and/ or closed off by overlayedresin-impregnated layers as at numeral 27 before curing, or otherwisepassed in a permanent, water-tight manner through holes formed at thebottom of the trunks side walls preferably at the level of the innersurface of the bottom of'the hull, as best shown in FIG. 2. Thisplacement of the pivot pin, which is preferably of brass, stainlesssteel or other in-corrodible metal, allows the major stress due to theweight of the centerboard to be carried by the hull bottom itself,rather than by the side walls of the trunk.

As indicated by dotted lines in FIG. 1, the centerboard can be droppedthe maximum amount corresponding to degrees from its upper or full lineposition, by paying out the pennant 16; in practice, it would be droppedto some intermediate angle depending upon sailing conditions and thejudgment of the user. To permit this pivoting action, the forward uppercorner of the board is rounded as at 28 on a circular are centered onthe axis of pin 26, and if the board is a close lengthwise fit withinthe trunk, the rearward edge is rounder or chamfered as at 30 about thesame axis. The height of the board is preferably equal to or slightlyless than the clear height of the trunk, so that no part of the boardprojects beneath the bottom of the hull when the board is raised.

The connection between the board 20 and the pivot pin 26 is by means ofa removable pivot block 32, best shown in FIGS. 3 and 4. This block fitswithin a rectangular notch or mortise in the lower edge of the board,the notch being just sulficiently longer than the block to allow it tobe tipped downward out of the notch when its fastening screws 34 havebeen removed. The lower edge of the block 32 is flush with the bottom ofthe board 20 (and hence with the bottom of the hull) so that there areno downward projections to be struck or to interfere with the propersupport of the hull on a carrier or the like, or when the boat isbeached or is grounded. The block 32 may be made of wood, marine bronze,stainless steel or the like, but I prefer to employ Delrin (an acetalresin) which simplifies the manufacture of the blocks in quantity.

It will be observed, in FIG. 3, that the rearward edge of the block 32has a rearwardly-opening semicylindrical slot or groove 36, sized to fitsnugly about the fixed pivot pin 26. Actually, the slot 36 is not trulysemicircular, but has a semicylindrical bottom of pin radius, beingrecessed into the body of the block to a greater depth than the radiusof the pin, the mouth of the slot being inclined downwardly at an angleof about 10 degrees, as indicated in FIG. 3, to assure seating of .thepin against the bearing block by gravity. Moreover, the upper rearcorner of the block 32 is rounded about the pin axis, as at 38, so thatthe block can be swung downwardly about the pin, as indicated at arrow Ain FIG. 3, when screws 34 are removed, to allow the block to be rotatedon the pin until it can be slid out lengthwise from the notch or recessin the centerboard. To permit this rotary motion, the lower rear cornerof the block 32 is chamfered at an angle of about 24 degrees (indicatedat 40) to avoid binding against the after end of the notch.

It is obvious that the rounding at 38 can be obviated if there is aslight clearance between the top of .the centerboard and the undersideof the top of the trunk 12, as indicated at 42 in FIG. 1, so that theboard can be raised slightly when the upper left corner of the blockstrikes the top of the recess from which it is being withdrawn.

The centerboard operation will be clear from what has already been said.When the board is lowered by paying out pennant 16, and the boat isunder way, the board can tilt rearwardly in case the bottom or otherobstruction is encountered, but it cannot in any case drop free of thetrunk, because the pivot pin is surrounded by the board and pivot block32 acting in concert. This secure fastening is retained when the boardis raised to its upper position also. When it is necessary to remove thecenterboard, this is easily done from beneath the boat, by raising thecenterboard and withdrawing the fastening screws 34 (which may bestainless'steel screws of the selftapping type for glass fiberconstructions, or wood screws for wooden boards or machine screws formetal boards) to allow the block 32 to be tipped down and slid out ofits recess. Even now, however, the centerboard will not fall out, as thefixed pivot pin will continue to support it. The board is now rotateddownward out of the trunk to an angle such that it may be moved towardthe stern of the boat (to the left in FIG. 1) so as to clear the pivotpin and thence be lowered free of the boat, and the pennantdisconnected. Replacement @merely requires the reversal of theseoperations, which is far different than the two-man operation heretoforenecessary wherein one man must be in the hull directing the vertical andhorizontal moveme it of the board by a second hand, in order to alignboard and trunk holes for pin insertion.

It will be observed that the block 32 can be produced in differentthicknesses to accommodate boards of the same variations, and in factcan be extruded or machined in extended lengths with the profile shownin FIG. 3 and then cut or sawed to size to minimize the inventory ofparts. In a typical size, for a centerboard of thickness, the block 32may be recessed into the board of an inch, and may be about 2 incheslong. In such a typical case, a pin diameter of /8" is adequate. It isto be noted that the screws 34 do not support the weight of thecenterboard, but merely secure the block 32 in place; the Weight of theboard when down is transferred to the bearing block at surface 43 andentirely carried by the pin 26 which, as noted, is effectively anintegral part of the centerboard trunk or the hull. It will also benoted that the material of block 32 is always strained in compression,regardless of the angle assumed by the centerboard.

A modified form of the invention is shown in FIGS. 5 and 6, and in whichform the fixed or integral pivotal pin is still a feature, although theremovable pivot block has been eliminated. Like parts are designated bythe same numerals as before, but the centerboard 20 is now formed with aright-angled slot 4-4, having a portion 46 which (when the board israised, as shown in solid lines) is vertical, and a portion 48 which ishorizontal and extends forwardly from the portion 46. At its forwardend, this horizontal slot portion 48 is terminated by a half-cylindricalbearing 5d of tough plastic cemented or mechanically attached to thematerial of the centerboard. As before, the pivot pin 26 is sealedintegrally and immovably in the material forming the walls of thecenterboard trunk. Layers 27 again designate an applied form ofwaterproofing permanently applied to the area during the construction ofthe hull.

In this modification, the length of the centerboard 20' is chosensufficiently shorter than the length of the trunk space, to allow aspace 52 so that, if the board is purposely moved to the forward end ofthe space, the board can drop free of pin 26 via slot portion 46. Toprevent this from happening during sailing, the pennant 16 is connectedto the board at such a point that its tension, induced by the weight ofthe board, pulls the board toward the stern (or to the left, as shown inFIG. 5). Even if the board 20' should be partly lowered (as shown indash lines), and the boat should be backed while the board is touchingbottom, the board could not move forward relative to pin 26 (to allowthe pin to reach the vertical slot portion 46), because the lip 54 wouldbe engaged behind the pin. The centerboard, when partially lowered,cannot ride up the inclined plane formed by slot portion 48, and becomedetached, because the centerboard cap or top acts as a stop for theradial end of the board 28. However, when removal of the board isdesired, it is held in its upper position, as shown, from beneath theboat, there being sufficient slack in the pennant to allow the board tohe slid forward, the slot portion 46 ultimately allowing the board todrop away from the pivot pin. To allow space for the pennant to moveforward with the centerboard during this operation, a housing at may beformed atop the trunk, shaped as shown to provide space allowing theennant to move to the forwardmost position indicated at 63.

To facilitate this motion of the board, the pennant may, as shown inFIG. 7, be secured at the bottom of a notch in the upper edge of theboard 20'', angled rearwardly as at 56 to allow this sliding motion, andhaving its other margin preferably curved (and optionally grooved as at58) to guide the pennant during ordinary raising and loweringoperations. As suggested by the dash lines at 64- in FIG. 7, the pennantmay also be passed 'reely through a hole in the top of the board if theboard is hollow in this region, and secured to the lower edge of theboard by swaging in a tapered hole or by other convenient fasteningmeans. It will be noted that, as before, the forward and upper corner ofthe board 22 is rounded at 28, which permits the downward swing of theboard only as long as the pin is at the closed end of slot portion 48.

While I have described my invention in considerable detail and inconnection with a variety of embodiments, so as to enable those skilledin the art to understand and to practice the same, I do not wish theinvention to be limited to the details thus given, except as may berequired by the scope of the appended claims.

What is claimed is:

I. A centerboard construction for boats, including a pivot pin fixedlysealed in an open-bottom centerboard trunk, said pin being disposedathwart said trunk near its connection with the hull of the boat andforward of the lengthwise center of said trunk; said centerboard beingarcuate at its forward corner with an arc center at the pin axis; saidpin passing within a downwardly open recess in the lower edge of saidcenterboard and substantially in contact with one vertical wall of saidrecess; an edge-notched bearing block substantially filling said recesswith the margins of its edge notch substantially encompassing said pinabout its region away from said wall of said recess, and fastener meansfor removably securing said bearing block in said recess, and forthereby securing the centerboard to the pivot pin and to the boat.

2. A centerboard construction for boats, in accordance with claim 1, inwhich said fastener means comprises at least one screw passingvertically through said bearing block and into the material of saidcenterboard.

3. A. centerboard construction for boats, in accordance with claim l, inwhich said bearing block is chamfered at its lower corner adjacent itsedge notch, to facilitate swinging removal thereof.

References Cited by the Examiner UNITED STATES PATENTS 11/1867 Corbett1l4l32 2/1884 Center 1l4132

1. A CENTERBOARD CONSTRUCTION FOR BOATS, INCLUDING A PIVOT PIN FIXEDLYSEALED IN AN OPEN-BOTTOM CENTERBOARD TRUNK, SAID PIN BEING DISPOSEDATHWART SAID TRUNK NEAR ITS CONNECTION WITH THE HULL OF THE BOAT ANDFORWARD OF THE LENGTH WISE CENTER OF SAID TRUNK; SAID CENTERBOARD BEINGARCUATE AT ITS FORWARD CORNER WITH AN ARC CENTER AT THE PIN AXIS; SAIDPIN PASSING WITHIN A DOWNWARDLY OPEN RECESS IN THE LOWER EDGE OF SAIDCENTERBOARD AND SUBSTANTIALLY IN CONTACT WITH ONE VERTICAL WALL OF SAIDRECESS; AN EDGE-NOTCHED BEARING BLOCK SUBSTANTIALLY FILLING SAID RECESSWITH THE MARGINS OF ITS EDGE NOTCH SUBSTANTIALLY ENCOMPASSING SAID PINABOUT ITS REGION AWAY FROM SAID WALL OF SAID RECESS, AND FASTENER MEANSFOR REMOVABLY SECURING SAID BEARING BLOCK IN SAID RECESS, AND FOR THERE-